It is often necessary in semiconductor processing to remove or etch dielectric films from a substrate surface. Various etching processes are available to etch different materials and geometries at different rates. Considerations for choosing the appropriate etch process include etch rates, selectivity to other materials, by-products, and ability to finely control the process. Regarding etch rates, rates for the material to be removed and rates for the material to remain at various geometries may be considered. Some etch processes are isotropic, etching evenly at all surfaces. Others are anisotropic. A higher etch rate is usually preferred, accompanied by a lower etch rate for the material intended to remain. This etch selectivity may be based on material properties and chemistry or geometries, e.g., whether the material is located on a sidewall or a field region. Sometimes compounds generated by the etch process, e.g., in some plasma etching processes, can redeposit and in some cases cause integration issues. Thus the by-product of the etching process and its removal from the processing area may be considered. For etching thin films or specific geometries, the ability to finely control the amount etched is an important consideration.
An etch process may be a step in a deposition process, such as in gap fill of shallow trench isolation (STI), inter-layer dielectric (ILD), inter-metal dielectric (IMD), and pre-metal dielectric (PMD) features. High aspect ratio features of narrow width are filled by depositing material into the bottom of the feature while removing, in an etch-back process, deposited material in areas that may obstruct further bottom deposition.
As film thickness and feature sizes continue to shrink, improvements in etch and etch-back processes to increase etch rate, selectivity, and reduce by-product issues, while maintaining excellent process control continue to be sought.